Gasification of Carbon by Carbon Dioxide in Fluidized Powder Bed grated. A graphical correlation of t h e integral, applicable t o normal conditions of fluidization, i s presented. For each carbon k~ rises rapidly w i t h t h e temperature, whereas both kz and k3 fall. A t low temperatures, as equil i b r i u m of t h e gas m i x t u r e w i t h t h e carbon was approached, t h e experimental conversions f e l l f a r below t h e values calculated f r o m t h e equation. A t high temperatures and low conversions, t h e rates found experlmentally were f a r higher t h a n those calculated f r o m t h e equation. Use of t h e correlations outside t h e range of t h e data is correspond ing Iy hazardous.
Comprehensive data are presented on t h e reaction rates
a t atmospheric pressure of carbon dioxide w i t h t w o types of carbon under fluidized powder conditions over t h e t e m perature range f r o m 1475" t o 2000" F. Mechanical operat i o n was smooth and satisfactory. The data have been oorrelated by a n equation of t h e Langmuir type, carbon dioxide reduction rate per unit q u a n t i t y of carbon in t h e
hPco* , where f o r each carbon t h e k I k2pr.o kdprni terms are functlons of temperature only. Because high conversions were secured, t h e equation had t o be intebed =
+
+
W. K. LEWIS,
E. R. GILLILAND,AND GUY IT. MCBRIDE, J R .
M A S S A C H U S E T T S I N S T I T U T E OF T E C H N O L O G Y . C A M E R I D Q E . M A S S .
S
carried into the reactor proper through a n inner concentric 0.125inch tube. The gases from the top of the column were conducted through a 1-inch copper line first into a separator (about 5 inches inside diameter X 5 inches straight section with flat top and 60" included angle cone bottom) and then into a cyclone of the same dimensions. Both cyclone and separator were fitted on the bottom with plug valves for solids removal. The gases passed next through a 3-inch inside diameter X 10 inches long glass wool filter, thence through an orifice for measurement of total gas flow. The temperature of the gas was taken downstream of the orifice by a mercury-in-glass thermometer inserted into a well in the line. The gas inlet system was manifolded as indicated, with individual, calibrated orifices for the various streams.
I N C E t h e introduction several years ago of the fluidized solids technique for catalytic cracking of oils, t h e carbon deposited on the catalyst in t h a t system has been burned off successfully in the catalyst regenerative step of the process. This operation has been of necessity conducted at low temperatures and it became highly desirable to explore the possibilities of reaction of carbon with gases at higher temperatures. It was particularly important to study the reactions with carbon dioxide and steam. because of the possibilities of using these gases in the formation of producer gas and water gas (9). This laboratory therefore initiated at the end of the war a n extensive program along this line. The work was started by Graham (6) and the purpose of this article is t o report the most recent results on the carbon dioxide reaction.
Procedure. T h e coke or anthracite was crushed, screened, and then recombined to the following size distribution: United States Standard mesh % by wt.
E X P E R I M E N T A L TECHNIQUE
The materials studied were anthracite from the Tamaqua colliery (IO),Lehigh Coal and Navigation Company, Lansford, Pa., and retort coke. The temperatures were varied from 1475O to 2000" F., at an average total pressure of about 1.1 atm. T h e partial pressure of inlet carbon dioxide was varied from about 0.05 t o 1 atm. It was mixed with nitrogen and in some cases with carbon monoxide. co 4
Apparatus. T h e apparatus used in this work is shown in Figures 1 and 2. The reactor itself was a 7-foot X 1.7Sinch inside diameter, Type 310 steel tube with 60' conical bottom and enlarged top, wound with 0.1875 X 0.040 inch Kanthal A-1 resistance ribbon embedded In alundum cement (Norton ILA. 1161). The tube mas equipped with pressure taps as shown and with thermocouples with leads insulated clear to the center of the tube. The wound reactor tube was suspended inside a 12-inch diameter cylindricid sheet metal shell and the annular space filled with insulation. The solids feed system consisted of a copper hopper with plug valves top and bottom connected by a flexible tube to a vibratory feeder to regulate the flow. The solid passed from the feeder into a vertical flexible feed leg, from the bottom of which it was entrained by the entering gas stream moving at high velocity arid
-20+50 6
-50+60
10
-60f100
48
-100+200
31
-200 5
This feed then was dried in air at 110" C. before being charged.
1
Figure I .
1213
Diagram of apparatus, 1.78 Inches lnside Diameter
1214
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 41, No. 6
was highly satisfactory throughout. It is well recognized t h a t small units of this sort require more attention on the part of the opcrator than larger units but the experience of the runs here reported demonstrates t'he complete practicability of this method of reacting carbon with gas. On the other hand, fluctuation in pressure drop across the bed is charactexistic of fluidization and is large percentagewise in a relatively s h a l l o w b e d s u c h as this. This makes dificult an accurate determination of the solids content of the bed, which in turn lessens +die reproducibility of the reaction rat,e data. RESULTS
T o initiate a run, the temperature of the empty reactor was first raised to a point 200" to 300" F. above the intended reaction temperature. Sitrogen Tvas admitted a t such a rate that the superficial gas velocity in the reactor was approximately 0.7 foot per second and bleed nitrogen vias introduced through the pressure taps to keep them open. The solid feed was begun by opening the valves underneath the feed hopper and starting the vibratory feeder a t a low rate to deliver coal to the inlet gas line. As the bed increased, the thermocouples were successively covered. Temperature was adjusted to the desired reaction level by means of the heating coil. Before admitting carbon dioxide to the bed, both coal and coke were fluidized for approximately 2 hours in a stream of nitrogen a t the temperature and gas velocity at. which the reaction was to be run. During the coking period, the coal feed x a s continued and the exit coal overflowed into the solid separators and was ret,urned to the feed system manually. About one and a half times as much coal was treated in this manner as was anticipated n-ould be required during the batch data run to follow. At the close of the coking period, the amount of carbon in the bed was adjusted to the desired amount and thereafter the bed was run batchlvise-that is, carbon was neither added nor removed (except t h a t a slight amount blew over during the run and it was occasionally necessary between data points t o add carbon to the bed in order to increase the degree of conversion). After adjusting the bed, the inlet gas composition was set a t t,he desired value and, after a period of 15 to 20 minutes a t a given gas coniposition and steady temperature, all the requisite readings were taken and a gas sample was withdrawn from the exit gas line. Each such set of readings Tvith its accompanying gas analysis was considered a data point'. T h e gas samples from which the decomposition of carbon dioxide was calculated were withdrawn as noted above. These samples were collected over a 20% sodium sulfate-5% sulfuric acid solution and were stored in glass between stopcocks unt,il analysis. Analysis was conducted over mercury by the standard Fischer technique. Proximate analyses were made of the virgin anthracite and coke, of the coked solid beiore reaction, of the column residue after reaction, and, if necessary, of the column contents during reaction. These analyses were carried out according t o the A.S.T.11. Sta.ndard Technique D-271. The mechanical performance of this equipment in operation
The numerical results of the present investigation are found in Tables I to S inclusive. They show the operating conditions, the gas rates and compositions and the carbon content of the bed. Inspection of the data makes i t obvious that in each case the measured exit gas rate can be checked from the measured inlet gas rates by either an oxygen or a nitrogen balance. The degree to which these results check is an excellent criterion of the dependability of the data. I n many cases, owing to the operating conditions employed, the amount of oxygen or nitrogen in the exit gas, shown by its analysis, is low. I n such cases, a small numerical error in that analysis can result in a large fractional error in the calculation of the balance. I n consequence, use was made of such an element balance only in case the quantity of the element in the exit gas was a t least 25%. The material balances thus computed check in most cases within better than 5%. Tho overhead gas lines developed occasional minor leaks, which, until detected and remedied, result'ed in low values of the directly measured outlet gas. Such runs were not discarded because there was no ground to question the dependability of the out,let gas analyses or the inlet gas measurements. The general dependability of t,he data seems beyond question. As already stated, the carbons were fluidized in nitrogen for 2 hours before carbon dioxide was introduced. Particularly in the case of anthracite, the carbons showed abnormally high reactivity when the flow of carbon dioxide was first st'arted. This was probably due bo a residue of the volatile combustible matter which is far morc active than the main body of the carbon, but which is oxidized off the carbon in a short time by the carbon dioxide. hbnormally high initial points were therefore discarded. The analyses of t,he product gases consistently showed small amounts of hydrogen. I n the case of coked anthracite, a not inconsequential amount of hydrogen was leit in the carbon a t the end of the coking operation in nitrogen. This hy-drogen apparently was worked out of the carbon slowly as the operation proceeded. It may be that there were traces of water in the inlet gases, but it is believed that even in the case of retort coke most of the hydrogen in the gas produced was from t,he residual hydrogen content of the coke itself. This hydrogen therefore was neglected in the computations. The over-all reduction rate of the carbon dioxide obviously can be calculated from these data in a variety of ways. However, the inlet fiow rate of the carbon dioxide, no,was in all cases measured directly. Multiplying this by F ,the fraction of the entering carbon dioxide reduced, as shown by the exit gas analysis, either alone or in connection with the other data, gives the total ratJeof reduction of carbon dioxide per unit time, noF. In order to cor-
June 1949 1215 m m
:o?y ' QM m
. .. ..
.
.
,
.. .. ..
. . . . .. .. .. ..
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I
.
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. . . .
.. .. .. .. .. ... ... ...
-
a X A
E
4
-0
0
E
E. 2 %s
3
1 rn
Vol. 41, No. 6
INDUSTRIAL AND ENGINEERING CHEMISTRY
1216
.. .. .. .. .. .. . . . . . . ... ... ... ... ... ...
... ... ... ... ... ... ... . .. ., ,. ,. .. .. *
. . . . . . . .. .. .. .. .. .. ..
. . . . . . . .. .. .. .. .. .. .. cori-
.. .. .. .. ... ... .. .
.
.
+
.. .. .. .. .. .. . , . .
.
N 0; 0; i.2
o
. . . .
N m m d N O l N
..I .. I .. ~.. .. I .. I.. .. I.. , .. r ..l ... ... ..
*
.. .. .. .. .. .. .. ,
*
I
,
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o
o
o
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"~~
~
.
INDUSTRIAL AND ENGINEERING CHEMISTRY
June 1949
1213
given carbon, temperature, and partial of the compressures 0.8 ponents of the gas in contact with the car0.7 bon, the reduction rate should be pro9 portional to the total 0.6 amount of carbon in the bed, w,the rate 8 0.5 was always comp u t e d a s noF/w. This in turn was plotted for each run against the inlet partial pressure of carbon dioxide, poco,. Characteristic results are shown graphically, Figures 3 and 4 giving F and Figures 5 and 6 giving n$/w 0.I plotted against poco,. Inspection of these Po cot ATM curves shows t h a t the 0 reaction rates a t high 0 0.2 0.4 0.6 0.8 1.0 I2 Figure 3. F vs. pKol temperatures, as is t o Po cop ArM. Anthracite a t 1475' and 1900" F. be expected, are far Figure 4. F vs. poco2 higher than at low, relate reduction rates thus computed for difMoreover, for each Coke a t 1600O and 1900' F. ferent conditions of operation, i t is highly set of operating condesirable t o work experimentally with a single ditions, the rate curve independent variable. I n these runs effort was made to for dilution of carbon dioxide with nitrogen lies above t h a t for dilukeep temperature, total pressure, total inlet gas flow rate, and tion with monoxide. This fact of itself demonstrates t h a t monoxamount of carbon in the bed all constant throughout a given run, ide exerts a depressing effect on reaction rate. However, the relachanging the partial pressure of the carbon dioxide in the inlet gas tive distance between the two curves is far greater a t low temfrom point to point during the run by varying inlet carbon diperatures than at high. This means t h a t the relative deprcssing oxide flow rate, no, and holding total pressure constant by dilution ' effect of carbon monoxide on the rate of reduction of carbon of this carbon dioxide with nitrogen for one set of points and with dioxide by carbon decreases quite rapidly as temperature rises. carbon monoxide for another. H a d it been possible to maintain I n other words, when one employs operating temperatures sufficonstancy of all these factors in a given run, for each diluent the ciently high t o give high reduction rates, the choice of those concarbon dioxide reduction rate should have been a unique function ditions of itself reduces the blocking action of monoxide on the of the partial pressure of the inlet carbon dioxide. Since, with rate of reaction of the dioxide with the carbon, I
0 9 ,
I
3
3 e
t
I
I
I
1 P
0 k
I2
I2
10
10
6
6
6
6
2.0
20
4
4 1.5
I S
c
2
2
21 B 0.5
0
4
213
Y
8
05
0
0 0
02
0 4
06
0 8
10
Po c o t , Figure 5. mF/w
VI.
pocos
Anthracite a t 1475' and 1900' F.
1.2
0 0
02
0 4
06
0 8
10
poco, ,A7-M noF/w VI. poCo2
Figure 6.
Coke a t 1600° and 1900'
F.
12
INDUSTRIAL AND ENGINEERING CHEMISTRY
1218
Table 1 1 1 . Date Barometer, in. H g Observation time, hr./min. Sample No. Reactant Inlet gas (corrected for impurities), lb. moles/min. x 1 0 4 Nitrogen bottom Nitrogen taps Carbon dioxide bottom Carbon monoxide bottom Exit gas analysis Oxygen Carbon dioxide Hydrogen Carbon monoxide Nitrogen Exit gas, lb. moles/min. X 104 Carbon in bed, lb. atoms r bottom. at.m. a top, atm. Sieve analyses (United States Standard mesh) 20 -20 40 60 -40 -60 f 100 -100 140 -140 200 200
-
+ + + +
Date Barometer, in. Hg Observationtime, hr./min. Sample No. Reaotant Inlet gas (corrected for impurities), lb. moles/min.
29.24 1330 w1 COz
29.24 1340 w2
COe
O;k8l 5.17
01581 5.23
0.5140 0.581 4.67
. . . . . . . . . 0.002 ...
0.001 0.341 0.015 0.559 0.084 8.30 0.256 1.135 1.034
0.346 0.015 0.548 0.089 8.41 0.252 1.137 1.038
.
...
.
0,012 0.527 0.151 8.17 0.244 1,128 1.032
0.306 0.588 6.81 0.239 1.121 1.027
. .
.
. . . . . . . . . . .
0.577 1.239 3.91
0.09 0.677 1.238 3.91
0 : itio 0.007 0.802 0,592 6.81 0.237 1,121 1.028
0.001 0,159 0.015 0.702 0.123 6.33 0.237 1.117 1.024
0,002 0.111 0.016 0.748 0.123 6.32 0.235 0.404 1.024
0,001 0.114 0.017 0.744 0.124 6.30 0.235 0.392
... ...
...
...
...
... ...
, . .
, . .
...
... ...
...
...
0: iio
0.017 0,705 0.118 6.48 0.235 1.117 1,025
w9
COz-CO
,..
.
I
. .
... . .
,
.
.
,
...
...
30.27 2100 IT22
29.99 1530 Vi23 COZ
0.586 2.654 2.333
0.057 0.586 3.554 1.627
0,026 0.586 4.506 0.748
0.586 4.53 0.760
0,026
0.013 0.586 4.843 0.366
0.013 0.586 4.792 0.366
0:589 O:k89 5 , 1 5 5 5.190
01298 0.010 0.599 0.093
0,001 0.301 0.009 0,592 0,097
0.001 0,347 0.011 0,548 0.093
0,001 0.356 0,010 0.546 0.088
7.60 0.228
8.02 0.212 1.162 1.076
0.586 2.693 2,333
0,003 0.062 0.016 0.789 0.130
0,001 0,067 0.018 0.781 0.133
0 : 222 0.012 0.658 0.108
0:22l 0.013 0.658 0.108
0.001 0.261 0,011 0.629 0.098
6.05 x 104, Carbon in bed, lb. atoms 0.242 bottom, atm. 1, 157 1.060 i~ t o p , atm. Sieve analyses (United States Standard mesh) 20 ... -20 40 ... -40 60 .., -60 100 -100 140 -140 200 - 200 a R u n 18 was abandoned.
3.96 0.239 1,161 1.065
6.83 0,232 1.160 1.066
6.77 0.230 1.159 1.966
7.31 0.216 1.164 1.070
7.58 0.233 1.163 1.069
. .
...
...
..
... ...
,..
..
(
.
.
.
.
I
... ...
...
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...
...
...
...
... I..
, . .
The fact that the inlet carbon dioxide in the nitrogen dilution runs was uncontaminated with carbon monoxide does not mean that there was no carbon monoxide present during the run. It does, however, mean t h a t t h e amount of carbon monoxide is limited to t h a t resulting from the reduction reaction itself. The recent work of Hinshelwood and his associates ( 3 ) has demonstrated the depressing effect of carbon monoxide on the reaction of dioxide and carbon and likewise has shown t h a t their reaction rate data can be correlated by means of an equation of the Langmuir type, where the rate per unit of carbon is equated t o klpco,/(l + k z p c o + k ~ p c o z ) . After careful preliminary study of the authors’ own data in the light of earlier work ( I , $ , 7 , 8) it was decided t o use an equation of the same form for this work. Since, however, the carbons used were entirely different from those used by other investigators, it was necessary to evaluate the constants of this equation for this work. This evaluation is complicated by the fact t h a t in many of the runs (indeed, in all of the runs of greatest engineering significance) the degree of conversion of entering carbon dioxide to carbon monoxide is high, so t h a t the partial pressures of the gases change greatly in their flow through the reacting mass. This obviously requires integration. Fortunately, however, the computational complications are in this case not serious. Work in this laboratory has demonstrated t h a t in a fluidized
.
I
4.65 0.577 0,596 ,..
0 025
0,005 0 147 0.823 6.13 0.233 1.115 1.024
...
4.13 20.64 59.63 1.59 7.34 3.67
1-6-48 29.99 29.99 29.99 1640 1605 1615 W24 W25 W26 Con coz-eo coz-co
7
0.154 0.586 0,656 4.357
...
.
30.27 2050 14’21
0.156 0.586 0.657 4.41
... .. ...
..
...
...
c o r c o c0,-co c o r c o coz-co cos-co coz-co coz-co coz-co coz-co
r
. ,
30.27 1955 W20
0.082
:
0 023 0,004 0.157 0.816 6.13 0.234 1.115 1.024
.. .
30.27 1940 W19
30.27 1555 W16
...
.. . . ...
12-4-47 30.27 1710 W17=
7 -
0.082
1.024
4.65 0.577 0.596
.
. . . .
...
...
...
30.27 1535 W15
+ +++ +
0.07 0.577 1.78 3.25
0.09
...
0.07 0.577 1.78 3.26
...
, .
30.27 1455 W14
x 109
3.455 0.577 1.734
, . .
... ...
. . . . . . . .
29.43 I605
...
..
. . . . . . . . . .
29.43 1540 W8 C0z-CO
...
0 : 098 0.008
7-2-25-48? 20.43 29.43 29.43 1615 1640 1850 m.10 Wll w-12 COz-CO COS-Nn COa-Nz
29.43 1530 W7 COz-CO
3.455 0.577 1.734
...
o:iio
0 ,316 0 ,011 0 ,521 0 .152 8.I8 0 ,248 1,128 1,031
.
0.5145 0.581 4.67
30.27 1410 W13
Nitrogen bottom Nitrogen taps Carbon dioxide bottom Carbon monoxide bottom Exit gas analysis Oxygen Carbon dioxide Hydrogen Carbon monoxide Nitrogen Exit gas, lb. moles/min.
W Anthracite
Summary of Data-Run
(Bed temperature, 1775O F.) 11-12-47 29.24 29.24 29.24 29.24 1400 1415 1440 1505 w3 W4 W5 W6 COe-Ne COa-Ne COz-Sz COz-h-2
r
Vol. 41, No. 6
,..
... . . I
,..
... ...
1.162 1.070
... ... ,,.
... ... ...
.
I
.
...
...
... ...
... I
zoo
.
.
0.350 0.010 0.561 0.087
0:353 0:i35 0,007 0.004 0,549 0.563 0.091 0.098
0.001 0.336 0,008 0,564 0.091
7.90 0.209 1.161 1.077
8.42 0,210 1.155 1.070
8.33 8.22 0,209 0.199 1.169 1.165 1.085 1.085
8.24 0.196 1.165 1.086
...
, . .
. . . . . .
0,002
..
, . ,
. . . . . . . . .. .., ..,
. . . . . . . . . . . . . . . . . , ,
.
,
..
,
..
. . . . . . . . .
I
I
0.006
0.589 4.837 0,388
4.00 54.50 24.00 3.50 4.00 10.00
...
0.006
0.589 4.837 0.381
I
, . .
. .
..
... ,..
I
I
1 I
7
I
I
104
T
---
Figure 7.
1
I
I
, e,,?,-/
Effect of Temperature on
&I
for Anthracite
Calculated f r o m F Intercept a t p o c o , = 0 Calculated from simultaneous equations
INDUSTRIAL A N D ENGINEERING CHEMISTRY
June 1949
powder operation, using the sort of conditions of flow which are essential to give satisfactory performance and employing, as in this work, a high ratio of depth t o cross section of bed, the amount of back mixing of the gas flowing u p through the bed is limited (6, 6). I n the preliminary interpretation of these results, the effect of any such back mixing has been ignored-that is, each element of gas rising through the bed has been assumed t o displace the gas ahead of i t and in turn t o be displaced by t h e gas behind i t without vertical mixing of the gases. On this basis, call n, m, and N the moles of carbon dioxide, carbon monoxide, and nitrogen, respectively, flowing upward per unit time through any horizontal cross section of the bed. The rate of reduction of carbon dioxide in any differential vertical element of the bed, containing a n amount of carbon, dw,is - dn =
1219
zoo
/oo 80
60
*
*?
40
kipco,dw
1
+ kzpco f
k3pcoa
The partial pressure of each component is the total pressure, T, times the ratio of the number of moles of t h a t component flowing past the section in question per unit time t o the corresponding total gas flow rate. Substitution, allowing for the stoichiometric interrelation of carbon dioxide and carbon monoxide, followed by integration between limits gives
4 .e
4 6
5 0
1 0 ' ,.* ., T
Figure 8.
---
Effect of Temperature on
klfor
Coke
Calculated from F intercept a t pocOz = 0 Calculated from simultaneous equations
Here me and no are the inlet flow rates of carbon mono- and dioxides, N is the constant flow rate of nitrogen, w is the total carbon in the bed, T is the total pressure (treated as constant), and F is the total fraction of the entering carbon dioxide which is reduced in the bed as a whole. I n t h e course of this work every term in this equation was determined experimentally, either directly or indirectly, except the three constants, kl, kz, and k3. For a n y series of runs at constant temperature, three points at different values of the variables are theoretically sufficient t o fix these three constants by solution of three simultaneous equations. By plotting the d a t a as in Figures 3-6, the constants were evaluated in this way. The smoothed curves were employed t o choose points as representative as possible. One point on each run was at the highest inlet carbon dioxide value. A second point was from the nitrogen dilution curve at the lowest inlet carbon dioxide which was still large enough t o give a dependable value of measured conversion. The third point was a monoxide dilution run where inlet monoxide and dioxide were about equal. This ensured a large monoxide depressant effect, without introducing gross errors due to low carbon dixoide conversion. The constants determined by this method of simultaneous equations are shown as functions of the temperature in the full curves of Figures 7-10. T h e dependability of these relations for the whole range of experimentation was tested by using in the general equation the values read off the smoothed curves of the constants just given to compute for each run the value of F t o be expected under its specific experimental conditions. These calculated values of F are plotted in Figures 11 and 12 against t h e values of F experimentally observed. As is t o be expected, the correlation is best at high values of the conversion, F . Small errors in the experimental measurements in the monoxide dilution runs under conditions giving low carbon dioxide conversion can yield gross errors in the F values stoichiometrically calculated directly from the data. Indeed, under such conditions, the data occasionally indicated negative conversions, despite the fact that the gases were still on the carbon dioxide side of equilibrium. Subject t o the limitations stated below, i t is felt t h a t the correlation is satisfactory for engineering use within the range of the data.
Inspection of t h e basic rate equation, which has been assumed, makes i t clear t h a t i t has two fundamental disadvantages. I n the first place, i t is impossible experimentally t o determine any one of its three constants directly without interference by the other two. This is because of the fact t h a t reaction rate can be measured only by allowing reaction t o occur and this particular reaction generates carbon monoxide, which in turn interferes with t h e reaction itself. The usual solution of the problem is operation under conditions of low conversion, but i t remains true t h a t in principle the determination of the constants requires the solution of simultaneous equations based on multiple conditions of experimentation. I n the second place, the constants are in high degree compensatory-in the sense that, for example, a high value of kl can be counterbalanced by a correspondingly high value of ICz or ka and vice versa. Similarly, kz and k~ can compensate each other.
3 it+---CALCULATCO FROM F INTEffCEPT
A?- %co* = 0 -CALCULATED FROM SlMUi TANEOUS EQUAT'IONS
I \.
IS00
I600
(700
I800
I900
0000
TFMPERA TURE ,OF.
Figure 9.
Effect of Temperature on A n t h racite
ke and ka for
INDUSTRIAL AND ENGINEERING CHEMISTRY
1220
Table IV. Date Barometer, in. Hg Observation time, hr./min. Sample No. Reactant Inlet gas (corrected for impurities), Ib. moles/min. X 1 0 4 Nitrogen bottom Nitrogen taps Carbon dioxide bottom Carbon monoxide bottom Exit-gas analysis Oxygen Carbon dioxide Hydrogen Carbon monoxide Nitrogen Exit gas, lb. moles/min. X 101 Carbon in bed, lb. atoms T Bottom, atm. r top a t m . Sieve'analyses (United States Standard mesh) 20 -20 40 -40 f 60 -60 100 -100 140 -140 zoo 200
-
+ ++ +
-
Anthracite
(Bed temperature, 1600° F.)
11-1S-17---J 30.21 30.21 1420 1430 Y11 Y12 COz-Nn C02-Nz
30.21 1700 Y25 C02rN2
30.21 1710 Y2A
4.35
4 . 3 ~ 0.579
n.5ni
... 0 . nno
...
0.579 0.488 0 . nnn
n. 005
0.165 0.816 5.96 0.171 1.117 1.049
..
4.454
n.ooi
0.171 1,117 1.049
...
.. .
Table
V.
n.011
0.011
4.214 0.734
0.0 0.240 0,011 0.591 0.158 7.851 0.196 1,161 1,084
0.0
..
,..
...
... ..
...
...
..
... ..
4.46
0.501 0.588 4.461
...
...
5:+3 24.84 50.32 7.01 7.64
.., ...
sn
...
n ,229 0.012 0.594 0,164 8.013 0.157 1.162 1.085
5.94
30.19 1740 Y27 COz-CO
COz-Nz
n.588
0.013 0 . on2 0.162 n. 823
0.014
...
.
0.488
...
,
Y
S u m m a r y of Data-Run
VOl. 41, NO. 6
n.588
0.260 0.013 0.619 0.108 7.738 0.182 1,158 1.083
.. ..
...
S u m m a r y of Data-Run
Date Barometer, in. Hg Observation time, hr./min. Sample No. Reactant Inlet gas (corrected for impurities), lb. molor/min. X IO' Sitrogen bottom Nitrogen taps Carbon dioxide bottom Carbon monoxide bottom Exit gas analysis Oxygen Carbon dioxide Hydrogen Carbon monoxide Nitrogen Exit g a s , lb. moles/min. X 10' Carbon in bed, lb. atoms II bottom, atm. r top a t m Sieve'analyses (United States Standard mesh) 2n
++ 4060 -60 + 100 -100 + 140 -140 + zoo -zn
-40
-zoo
COz-CO
0.03s 0.588 2.444 2.45:
2.454
2.432
0.734
n.038 n.588 2.444 2.451
0 , no1
0.0
0.0
0.0
0.0
0.187 0,013 0.650 0,110 6.612 0.171 1.142 1.073
0.190 0.012 0.686 0.112 6.604 0.169 L ,142 1.074
0.115
0.116 0.009 0.447 0,428 6.555 0.198
1-28
COz-CO
n.ms 4.204
n,275
n.012
o.6m 0.106 7.646 0.178 1.151 i.mo
n.575
4.628
4.114
0.575 0.467 , . .
o i45 0 , nis '
0 :009
0,008
n . 743 0 . 1 4 5 n ,094 n ,838
7.778 5.344 0.174 0.116 1.134 1,092 1 . 0 ~ 31 . 0 4 8
...
1 . 4 7 4:ie 2n.59 19.05 52.94 4 7 . 6 2 17.65 23.81 7 . 3 5 4.76
.. , .
...
...
...
2.514
0.008 0.449 0 428 6.558 0.202
1 I58 1 078
1600
I700
1804
1900
2000
TEMPERATURE ,OF
Figure 10.
Effect of Temperature on Coke
k~and ks for
. . . . . .
1,168
... l
0 001 0 278 0 014 0 605 0 102 7 541 0.197 1 188
0 277 0,013 0.608 0.101 7,541 0 193 I 158
...
. .
.~
.
.
I
,
,
1
,
0 001
I 080
20:37 29.68
. . , 30.86
...
...
. t .
,..
. . ~
...
.
4.983
1 074
... ... ...
... _
4.965
1.07%
..
3.671 0.575 0.936
..
0.007
0.116 1,092 1.048
...
.
0.936
0.575 4.780
n:oig
o:iii
.."
0.016 0.748
5.906
0.095 8.057
0.112 1.097 1.055
1.084
i:m
..
21.47
..
i2.12 lL96 6.38
...
cop
0.575
n. Yon
5.549
1450
AC-6 ,
0.273
0 150 0,835
30.10
3.671
o.on8
o.no8
-----
__ ._ 29 72 1600 AC-5 COz-N2
0.172 1.150
-2-29-4830.10 30.10 1520 1535 AC-7 .4C-8 CO*-CO corco
2.739
ii04 n.011 0.750 0.135 6.225 0.105 1.111 LO71
0.014 0.776 n.123 6.253 0.102 1.111 1.Oi2
.,
1:iu 19.05 50.79 19.05 7.94 1.59
n.042 0.575 1.851
0.042 0.575 1.851 2.739
.
.
..
.. .
o:O&
. . I
...
... ...
... ...
...
._,
...
8.03 6.79 4.32
-
30.10 1545 4C-9
30.10 1550 AC-10 COa-CO
0.027 0,575 2.848 1.749
0.027 0.575
cos-CO
o:iiS
n.010 0.748 0.117 0.729 0.100 1.115 1.077
... ... .., ... , .. ... ...
2.848
1.749
n:iio
0.011 0.754 0.115 6.756 n.098 1.115 1.077
...
5.33 29.33 42.67
16.00 6.67 , . .
\Vere the data perfect and the equation valid, this would pose no problem, but in work such as is reported here, where it is impossible to maintain complete constancy of operating condif ions, these limitations constitute a serious handicap. While complete resolution of this dilemma is impossible, an approach can be made. Inspection of the basic differential equation shows t h a t in any run in which there is no initial carbon monoxide-that is, nitrogen dilution-and the initial carbon dioxide partial pressure is sufficiently low, so that neither monoxide nor dioxide can ever be high, the denominator becomes substantially unity and the equation simplifies to -dn = k l p c o 2 d = ~ k i m d w / e , where E is the total gas floiv rate, substantially constant under these conditions. Integration between limits. followed by elimination of no/n through the relation, Fno = n0-71, gives k l w ~ = e l n ( l - - F ) . Granting constancy of the ratio, w/e in the points of Figures 3 and 4 and that these F curves can be dependably extrapolated to the proper values a t poco, = 0, this equation makes it possible t o evaluate kl independently of kz and IC,. -4n alternative method of extraDolatinr F to its value a t zero inlet carbon dioxide in the nitrogen dilution runs is to draw the slope of the curve of noF/w against pocoz at the origin. Calling this initial slope 01, the corresponding valuc of F is C L ? T X / E . Extrapolation of this sort involves uncertainty; indccd, heI
I500
o:iis o:bis
.."
.. ...
.. ..
CO1
0.588
2.514
.,.
30.14 2130 Y34
30.14
2120 Y33 COz
A C Anthracite
...
... .., .., . .
n.588
..
(Bed temperature, 2000° F.) -2-28-48 29.72 G . 7 2 29.72 29.72 1455 1525 1535 1550 AC-I AC-3 AC-2 AC-4 CO? COv-N? COr-Xz Con-Nz 1.114 0.575 0.467
..__I
30.15 2045 Y32 COz-Nz
.. ... ..
2-4-.48--..... 30.17 30.17 1815 1820 Y29 Y30
30.15 2033 Y31 COP-CO COz-liz
...
..
...
19 1747
INDUSTRIAL AND ENGINEERING CHEMISTRY
June 1949 l 0
i.0
0.1
0.1
0 OJ
0.0J
1221
2 P
d
Y
IP,
0.oo/ 0 Ol ~o€ls&Q"m
Figure 11.
Calculated
FOEShR VEO
F VI. Observed F for Anthracite
cause i t involves allowance for the curvature as the curve leaves the origin, one is tempted t o impute a n influence of ks and ks on the extrapolation. However, this graphical approach avoids the presuppositions as to curvature which are implicit in the assumed form of the basic equation. It constitutes an independent approach t o evaluation of the constants. The F curves for both anthracite carbon and retort coke have been extrapolated to zero inlet carbon dioxide by this method at each temperature level and the values of IC1 calculated. I n each nitrogen dilution run, F was calculated using the exit gas analysis alone. Where monoxide was the diluent, the exit gas analysis was still used but was supplemented by t h e ratio of the two directly measured quantities, mo and no. The results are shown as t h e dotted lines of Figures 7 and 8. The values are somewhat lower than those obtained by the method of simultaneous equations, shown by the full lines on the same diagrams. This method of estimation of k, independently of k z and k3 now makes it possible t o use graphical correlations of the data which can help in evaluating kl and kl numerically as well as in testing the validity of the underlying assumptions and detecting trends in the results. Take, for example, the carbon monoxide dilution runs at a temperature level low enough so t h a t conversion of the dioxide is always small. This means there is little change in any of the partial pressures as the gas flows up through the bed, so that average values can be employed for them. Hence the basic equation integrates into klpco,w/noF = 1 kzpco k3pco2. Since in these runs the sum of the partial pressures of carbon dioxide and monoxide was kept at a substantially constant value, ?y' (n' is somewhat less than n because of the tap nitrogen bled in), this equation becomes klpcoZw/noF = 1 k m ' - (kz - k 3 ) p C O ~ . This means that if the loft hand side of this equation be plotted against prop, a straight line should result. Figure 13 shows that at high values of pcoz this is indeed true, but that at low values of pcoz the ordinates are abnormally high. These high ordinate points are all at low conversions, two of them at conversions of less than 1%, so that one might be inclined to discount the deviations as due to small experimental errors. However, the deviations seem far too consistent t o justify such an explanation. The vertical dotted line a t the left of the diagram has been drawn t o
+
+
+
Figure 12.
Calculated
F
vs. Observed
F
for Coke
1;4: a-'
0
0.2
0.4
0.6
0.8
1.0
A V'G. Pco,, ATM.
Figure 13.
Correlation for C O Dilution Runs a t Low Conversion Levels
Anthracite a t 1475O
F.: kt taken
as 3.85 X 10-4
correspond t o the equilibrium of the reduction reaction for the conditions of this plot. I n other words. carbon dioxide entering the reactor at this partial pressure would, in view of its accompanying monoxide, be at equilibrium. There would be no reaction whatever-that is, F becomes zero and the ordinate of the plot must become infinite. Because the basic rate equation as-
INDUSTRIAL AND ENGINEERING CHEMISTRY
1222
Table VI.
S u m m a r y of Data-Run
Vol. 41, No. 6
R Coke
(Bod temperature, 1475' F.) Date Barometer in. H g Observatioh time, hr./min. Sample So. Reactant Inlet gas (corrected for impurities), lb. molet./ min. X 104 Nitrogen bottom Nitrowen taps Carbon dioxide bottom Carbon monoxide bottom Exit gas analysis Oxygen Carbon dioxide Hydrogen Carbon monoxide Nitrogen Exit gas, lb. moles/min.
x 104.
Carbon in bed. lb. atoms bottom. atm. T top, a t m . Sieve analyses (United States Standard mesh) n?. T
dU
29.38 29.38 29.38 1550 1605 1645 R-11 R-12 R-13
cot
CO*-S2
COZ
5,495 O:k63 0:593 0.593 6.02 5.92 0.608
. . . . . . . . . 0.0
0.0
0.878 0.001 0.022 0,099
0.881 0.002 0,022 0.095
0.093 0.0 0.000
7.05 0.276 1.188 1.084
6.93 0.275 1.178 1.083
6.445 0.274 1.182 1.079
0.0
0.898
29.38 1655 R-14
29.38 1730 R-15
1-2-48 29.38 1745 R-16
29.38 1830 R-17
29.38 1840 R-18
29.38 1915 R-19
29.38 1930 R-20
co*-CO
cog-co coz-co coz-co
5.435 0.593 0.600
0.136 0.593 0.623 5.14
0.135 0.593 0.617 5.12
0.122 0 593 1.269 4,617
0.120 0,593 1.268 4.564
0.593 2.082 3.800
0.099 0.593 2.076 3.770
0.0 0.091 0.0 0.008
0.0
0.0
0.0
0.901
0.097 0.015 0.767 0.131
0.0 0 188 0 014
0.0
0.101 0.012 0.776 0.111
6.445 0.274 1.176 1.073
6.41 0.274 1.176 1.073
6.43 0.277 1.176 1.072
coz-Ii2
...
con-CO 0.100
coz-co
29.96 1430 R-21 C02-Nz
1-3-429.96 29.96 29.96 1440 1520 1530 R-22 R-23 R-24 C02-Nz
COZ
coz
4.165 0.594 2.037
4.120 0.594 2.018
0:b94
0:594
0.0 0.0020.001 0,293 0.884 0 . 8 8 5 0.004 0 . 0 0.0 0,017 0.017 0.018 0.686 0,097 0.096 6.61 0.280 1.193 1.087
...
0,307
0.001 0.306
0.011
0.008
0.685 0.113
0,191 0.012 0.677 0.120
0,573 0,109
0.563 0.122
0.0 0.289 0.005 0.021 0.685
6.63 0 276 1,176 1 072
6.57 0.276 1.176 1.072
6.65 0,273 1.179 1.076
6.61 0.271 1.177 1,074
6.71 0.282 1.193 1.087
30.10
30.10
30.10
1-5-48 30.10 30.10
1545 R-31
1555 R-32
1640 R-33
6.220 6.165
. . . . . . . . . .
7.20 7.15 0.276 0.274 1.202 1202 1.098 1099
+ 50 +++60 100 . 200
-20 -50 -60 -100 - 200
Date 7-1-3-48 Barometer, in. HE 29.96 29.96 Observation time;hr 1 min. 1605 1625 Sample No. R-25 R-26 Reactant COZ-NL COz-X, Inlet gas (corrected for imwrities), lb moles/min. x 10' Nitrogen bottom 3.013 2.993 Nitrogen taps 0.594 0,594 Carbon dioxide bottom 3 013 3.020 Carbon monoxide bottom ... Exit gas analysis 0 0 0,001 Oxygen 0.433 0.437 Carbon dioxide 0,001 Hydrogen 0.0 0 016 0,013 Carbonmonoxide 0.551 0.548 Nitrogen Exit gas, lb. moles1 min. X 104 6.565 6.565 Carbon in bed, lb. atoms 0,271 0,271 II bottom, atm. 1.187 1.188 T top atm. 1.085 1.086 Sieve' analyses (United States Standard mesh)
20 -20 -50 -60 -100 - 200
+ 50 + ++60 100 200
(contli.)
,-30.10
~
30.10
30.10 30.10
1755 R-36
1830 R-37
COz-CO
1700 1745 R-34 R-35 COz-Sz c 0 2 - K ~ COz-CO
COz-CO
Cot
0.598
0,014 0.598
0,6244 0.624 0.598 0.598
0.007 0.598
0.007 0.598
01598
0.568
4.103
5.269
5.269
5,580
5.550
5.755
5.755
6.22
6.18
1.993
1.990
0.892
0.888
...
0.472
0.474
0.004
0,001 0.585
0.0
0.002
0.2
0,001
0.004
0.0
0.0
0.139 0.096
0,020 0.021 0.188 0.188
0.818 0.001 0,069 0.111
0.002 0.816
0.006
0.003 0.753 0.003 0.141 0,100
6.40
6.90
6.91
7.00
6.95
7.05
0.285 1.196 1.088
0.281 1.205 1.099
0.279 1.205
0.278 1.206 1.101
0.276 1.205 1.101
0,273 1.206 1.103
29.96
29.96
1800
R-27
1810 R-28
145.5
R-29
1505 R-30
CO2-CO
COz-CO
CO2-CO
COz-CO
COz-CO
0,044 0.594
0,044 0.694
0,030 0.594
0,030 0.594
0.014
3.082
3.084
4.095
2.960
2.900
0.0
0,000
0.446 0,008
0,448 O.OOC,
0.584 0,006
0,422 0.124
0,430 0.111
0,300 0,106
0.298 0.110
6.72
6.63
6.54
0,271 1.188 1.086
0,272 1.191
0.286 1.200 1,092
1,088
38 14 8 74 20 62 17 54 14 96
sumed utterly fails t o provide for the slowiomn t o zero rate a t equilibrium, i t must break down as this vertical equilibrium line is approached. The actual experimental curve of this plot must approach the vertical equilibrium line asymptotically. The sound interpretation of the rapid rise of the valuer of the ordinates a t the left of this diagram would appear to be the brealrdonm of the basic rate equation employed in the neighborhood of equilibrium. Study of the data indicates t h a t this retardation dur t o approach t o equilibrium was only encountered in the lo^ temperature carbon monoxide dilution runs a t low dioxide concentrations. Inspection of the general integrated equation makes it clear that, once ki is known, for any given temperature a plot of
should give a straight line. Furthermore, all data points, whether the diluent is nitrogen or monoxide, should fall on the samc line. Figures 14 and 15 shorn correlation plots of this sort. The points on the left of these diagrams correspond to conditions of high con-
0.761
1,100
... 0.790
0.t91
30.10
1840 R-38
. . . . . . 0.0 0.880
0.0
7.02
7.06
7.05
0.273 1.205 1.102
0.372 0.271 1.206 1.206 ]..lo4 1.103
0.0
0.071 0.111
0.858 0.002 0.003 0.018 0.020 0.100 0.122
10 13 22 38 14
09
95 76 22 98
version. These points therefore represent data of maximum dependability. Because of this situation, a representative line was carefully drawn among these points and was assumed to constitute the best correlat'ion of the data. From such a line the constants k , and k3 for the ternperaturc in question can be evaluated immediately. I n Figure 14 the flatter of the two lines shown is computed using the value of k , obtained by the method of extrapolation described above. The last tvio points t o the right on this diagram fall far below the line which was determined by the points t o the left. Because t,here is no absolute assurance t h a t the values of ICI determined by extrapolation are more dependable than those determined by the method of simultaneous equations, the ordinat,es of Figure 14 were recalculated using the value of isl computed by the latt,er method. The last two points on the right hand side of the diagram still fall below the line corresponding to the other points, but their divergence from t h a t line has been greatly reduced. On the basis of this behavior, the higher value of /:, may be favored. However, before reaching final decision it is important to study the corresponding data on coke shown in Figure 15.
Vol. 41, No. 6
INDUSTRIAL AND ENGINEERING CHEMISTRY
1224
Table V l l l .
U Coke
S u m m a r y of Data-Run (Bed temmrature. 1775' F.1
Date Barometer, in. Hg Observation time, hr./min. Sample KO. Reactant Inlet gas (corrected for impurities), lb. moIes/min. X 104 Nitrogen bottom Xitrogen taps Carbon dioxide bottom Carbon monoxide bottom Exit gas analysis Oxveen
Figure 14.
~
_
U8
29.79 1805 Ull
29,79 1815 u12
29.79 1845 U13 CO*-Kz
29.79 1925 U14
0.09 0.582 1.07 3.93
0.07 0.582 1.77 3.27
0.07 0.582 1.77 3.29
3.49 0.584 1,73
3.50 0,584 1.73
4.71
0.53 0.584
0.002
0.717 0.116 6.19 0,2601 1,130 1.031
0.001 0.146 0,019 0.711 0.123 6.19 0.2620 1.130 1.031
0,201 0.016 0 . G60 0 121 6 33 0.2659 1.134 1.033
0,001 0.204 0.015 0.662 0.118 6.33 0,2649 1 134 1.034
,..
...
0.09 0.582 1.07 3.93
coz-co coz-co co2-co co*-co corn., co*-ii*
0 : i42
..... .
... .., ...
+
0
.
29.79 1745 u10
29.79 1715
0,025
Kitrogen Exit gas lb. moles/min. X 104 Carbon in bed, lb. atoms T bottom, atm. r top a t m Sieve'analyses (United States Standard mesh) 20 -20 4-50 -50 f 60 -GO f 100 -100 200 - 200
. ~ _ _ _ _ _ _ 11/8/47 _ _
29.79 1730 u9
29.79 1655 u7
I
I
I
1
I
I
2
3
4
5
~
o:ik
0,007
0,235 0.G1.5 6.67 0,2659 1.137 1 036
.. .. .. ... ...
,
0.584 0.52
4.71
0:564 5.28
0:033 0.005 0.127 0.835 6.17 0.2649 1,135 1.035
0.001 0.472 0,007 0,355 0.166 7.39 0,2592 1.145 1,047
0.001 0.530 0.006 0.368 0.098 7.44 0 2564 I 114 1 01;
..
...
.
o:i44 0.009 0.235 0.612 6.69 0,2631) 1,187 1.037
)
.
... ... , . .
.
. . , . .
1
I
.
.
...
. ,
I . .
co1-;2s
_
29.79 1940 Ul5 COY
1:iW
7.62 53.81 34.29 12.38
from the correlation line, the quantity of carbon, which should exist in the bed in order t o give the assumed conversion under the assumed conditions of operation, can be determined. It is clear that if an experimental point falls below the correlating line, this is equivalent to saying that the actual conversion was achieved x i t h a lower quantity of carbon in the bed than would be called for by the correlation. This in turn is clearly equivalent t o having the actual rate of reduction of dioxide greater than would be indicated by the correlation. I n other words, the loa. points to the right in Figures 14 and 15 indicate reduction rates above those corresponding to the correlation, which is based on the most dependable data available- namely. those for relatively high conversions. I n the case of the coke runs, unlike the anthracite, the use of the higher value of kl determined by the method of simultaneous equatioiis did not significantly improve the correlation of the lorn conversion points t o the right of Figure 15 with the high conversion runs to the left of t h a t figure. Keeping in mind the fact t h a t the lorn points t o the right i n Figures 14 and 1.3 always correspond t o low absolute reduction
Correlation of D a t a f o r Anthracite a t 1900" F.
As in the case of the anthracite of Figure 14, so also in the case of the coke runs, the points t o the right of the diagram fall far below the correlation line determined by the left hand points. I n both diagrams, these low-falling points all correspond to low absolute conversions. .4s already pointed out, the experimental dependability of such points is open to question, and is certainly less than the dependability of the data falling on the left of the diagrams. However, inspection of the plots shows that the deviations of these points a t the right are consistently unidirectional Furthermore, the deviations show a marked tendency t o increase as the values of the abscissas increase. Finally, the direction of these deviations is opposite to t h a t anticipated from study of Figure 13, where conversion slowed up to values far below those indicated by the correlation when, due to the combination of low amounts of carbon dioxide and high amounts of monoxide in the entering gas, the conversion reached lorn- values. The expression for the ordinates of Figure 15 shows that the quantity, to,appears only in the first term and does not appear a t all in the abscissas. Granting a run in which the flow rates of the entering gases and the degree of conversion of dioxide t o monoxide are knovn, the corresponding abscissa is fixed and by reading off the ordinate
f
( Z + + y ( T
Figure 15.
I
id
Correlation of D a t a for Coke a t 1900" F. kl
taken as 60 X
~
~
June 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY
1225 0 0 m d l m
-
:???m.?
~ m h c m a d N
... ... ... ... ... ... . . . . . .
.. .. .. .. .. ..
R$4 ?Yn!
i o 0
:
. . . . .
.. .. .. .. .. ..
r n W - 3 0 t-C.3-t 0 0 m 3 h 0 n LO ??????@?-!? . . . . ooooou3o'-
0
. . . . . . .. .. .. .. .. ..
. . . . . .
... ... ... ... ... ...
.. .. .. .. .. .. . . . . . .
n - N V
.. .. .. .. .. .. . . . . . .
. .. .. .. .. .. . . . . .
8280
. . . . . . .. .. .. .. .. .. . . . . . .
2 m
... ... ... ... ... ...
0
: : : : : : 0 0 u) 0
"i?? : 6 3 0 -
2:$2$,23%
????Y???? 3 0 0 0 0 0 0 ' -
w
.. .. .. .. .. ..
. .. .. .. .. . . . . . . .
Z 2 8 V
... ... ... ... ...
0 n -2m2v6 0
'? ?Oetis
. . . . . .. .. .. .. ..
%%Go 0
. . . . . .. .. .. .. ..
m h m o w
:sc??Y? SZ'$Z"
. . . . . .. .. .. .. ..
.. .. .. .. .. .. . . . . .
. . . . . .. .. .. .. ..
. .. .. .. .. .. . . . . .
.. .. .. .. .. . . . . .
... ... ... ... ...
... ... ... ... ...
2 B
4
-3 E
B
zrn
1226
INDUSTRIAL AND ENGINEERING CHEMISTRY Table X.
Vol. 41, No. 6
S u m m a r y of Data R u n AD Coke (Bed temuerature. 2000O F.I
Date Barometer, in. Hg Observation time, hr./min. Sample No. Reactant Inlet gas (corrected for inipui+ties),, lb. moles/'min. Nitrogen bottom Nitrogen taps Carbon dioxide bottom Carbon monoxide bottom Exit gas analysis Oxygen Carbon dioxide Hydrogen Carbon monoxide Sitrogen Exit gas, lb. moles/min. X 10' Carbon in bed, lb. atoms ?i bottom, atm. z top, atm. Sieve analyses (United States Standard mesh) 20 -20 f 50 - 5 0 -I-60 -60 C 100 -100 200 200
-
+
1710 1
x
104
29.81 1720 2
con
o:5s9 4.794
0:5li9 4 794
. . . . . .
0.000 0.172 0.020 0.718 0.093 7.482
o:i6s
0.017 0.724 0.091 7.482 0.171 0 . 1 7 2 1.161 1.098 1.097
...
3
coz-co
rates of carbon dioxide, due either to lon- concentrations of dioxide or to high concentrations of monoxide in the entering gas or combinations of these two factors, it may be suspected t h a t the basic differential equation breaks down under these conditions, probably in the sense of overplaying the depressing effect of monoxide on the reduction rate of dioxide where the ratio of monoxide t o dioxideis high Such anindication obviously means that extreme caution must be used in extrapolation of the data beyond the experimental range. On the other hand, from the engineering point of view, i t is a t least fortunate that the direction of the deviations makes the correlation conservative for purposes of design. Figures 9 and 10 show the values of k p and k , recommended for anthracite and coke, respectively, as computed by the two methods of estimating the constants described above. There is probably little to choose between the two sets of constants from the point of view of dependability. Inspection of Figures 7 and 8 makes i t clear t h a t the rate of change of the specific reaction constant, k,, is much greater for coke than for the anthracite carbon. The corresponding apparent heats of activation are -86,000 B.t.u. per pound mole for the coke, and -59,000 B.t.u. per pound mole for the anthracite. The values of kl for the two types of carbon become equal in the neighborhood of 1900' F., but the reactivity of the anthracite carbon is far higher under conditions of low temperature than that of the retort coke. Differences of this sort in the reactivity of different types of carbons are well known. Indeed, a t a given temperature level differences of a hundredfold have been reported. I t is well known t h a t a given carbon tends to lose in reactivity when heated t o high temperature levels. The coke used in this work was formed under high temperature conditions and its reactivity was presumably reduced thereby. The anthracite carbon used in these runs, however, was formed from the coal employed by a process of distillation which in all cases was carried out a t the same temperature level used for the reaction rate runs. The residue from anthracite distilled a t 1475 O F. had never been heated t o a higher temperature before its reactivity was measured. However, when the same coal was distilled and reacted at 1900" F., the residue presumably lost a great deal of reactivity due to the higher temperature t o which i t was exposed, before reaction rate was measured. The retort coke, having been deactivated by high temperature in the original process of its formation, did not regain reactivity a t lower temperature levels. Work now under way in this laboratory indicates that the reactivity of the carbon in the coke changes as the carbon is burnt off and the ratio of ash to carbon increases, but in the work here reported the maximum amount of the original carbon burnt off was
:SO0 ~
3-7-48 29 79 1810 1825
COrCO
COP-Nz
0.028 0 . 0 2 8 0 , 0 4 3 0 . 0 4 3 0.578 0.578 0.578 0.578 2 . 8 7 4 2 . 8 7 4 1 . 9 1 4 1.914 1.806 1.806 2 . 7 5 3 2 . 7 5 3
29.78 1835
-
29.77 1845 1855 9 10 COrNz
3.688 3.688 4 . 1 9 4 4 . 1 9 4 0.578 0.578 0.578 0.578 0 . 9 4 6 0 . 9 4 5 0.4fi8 0.468
......
... . . o,'i$o o:ii4 o.'iig o.'oio o.'i)iz . . . 0 . 0 1 7 0 . 0 1 4 0 . 0 1 6 0 . 0 0 8 0.006
......
,..
0 : 0 0 9 0:008 0 . 0 0 8 0.008 0 . 1 4 8 0.151 05 . 83 38 53 0 5 . 38 43 23
...
0.110
,
0.711 0.754 0.748 0.258 0.254 . . . 0 , 1 1 2 0.118 0 . 1 1 8 0 . 7 0 4 0.708 . . . 6.481 5.969 5.949 6.750 5.709 0 . 1 1 6 0 . 1 1 6 0 . 1 1 4 0.112 0.112 1.126 1.118 1.113 1 . 0 8 2 1 . 0 8 3 1.C75 1 . 0 7 6 1 , 0 7 2 1 . 0 7 1
. . . . . . .
4.83 9.09 19.36 18.15 45.17 4 7 . 7 3 26.84 2 2 . 7 3 4.83 2.27
29.80 1745 4
1740
0.110 1.106 1.066 1.066
29 ~ .7 6. 1915 1920 11 12 COrhz
3.189 0.578 1.421
3.189 0.578 1.421
0:0i6 0.006 0.346 0.602 5.658
O:Ok6 0.005
. . . . . .
0.344 0.605 5.718
0.108 0.108 1.112 1.073 1.073
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. ... . . . . . . . . ... . . . . . . . .
,..
. . . . . . . . . . . . . . . . . .
, . .
never high and it seems unlikely that the results wer? significantly influenced by this effect. Diagrams of the type shown in Figures 14 and 15 are convenient for purposes of design. At 1900" F. they make it possible to determine directly the amount of carbon required in the bed once the operating total pressure, the feed gas rates, and the desired carbon dioxide conversion are known. For the two carbons here studied additional correlation lines for temperatures other than 1900" F. can be drawn by the use of Figures 7-10. The reactivities of carbons from different sources and with different histories are subject to large variations. Consequently, for dependable results the specific characteristics of the type of carbon used must be determined experimentally. NOMENCLATURE
E = activation energy F = fraction carbon dioxide decomposed in a given run
k (with subscript) = constant defined by equations given carbon monoxide passing any point in reaction bed (Ib. moles/min.) X lo4 (subscript zero refers to entrance conditions) carbon dioxide passing any point in reaction bed (Ib. moles/min.) X lo4 (subscrbt zero refers to entrance conditions) nitrogen passing any point in reaction bed (lb. moles/ min.) x 104 (subscript aero refers t o entrancr conditions) gas partial pressure, atmospheres, subscript denoting gas and location quantity of carbon in bed, lb. atoms total pressure, atmospheres absolute temperature, O R. LITER A TU R E C I T E D
(1)
(2) (3) (4) (6) (6) (7) (8) (9)
Clement, J. K., Adams, L. H., and Haskins, C. N.. U . S . RUT. Mines Bull. 7 (1911). Dubinsky, S. M., M . Y . thesis. ?4ass. Inst. Technol. (1932). Gadsby, J., Hinshelwood, C. N., and Sykes, K. W., P r o c . Boy. Soc., 1 8 7 A , 129-51 (1946); Gadsby, J., Long, F. J . , Sleightholm, F., and Bykes, K. W., Zbid., 193, 358-76 (1948). Gilliiand, E. R., and Mason, E. A , , IND.Ex+.CHEM.,41, 1191 (1949). Graham, H . 8., S0.D. thesis, Mass. Inst. Tech. (1947). Kennel, W.E., M . S . thesis, Mass. Inst. Tech. (1946). Mayers, M. A . , J . A m . Chem. Soc., 56, 70-6 (1934); Chem. Rev., 14, 31-56 (1934). Mayers, M. A., J . A m . Chem. Soc., 61, 2053-8 (1939). Powell, A. E., et ai., I N D . ENG.CHEM., 40, 547-766 (1948).
(10) Sayers, R. R., et ai., U . 8. Bur. Mines Tech. Paper No. (1944). RECEIvEn January 3, 1949.
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